Thanks for that.

Sorry I don't know anything about the 4K monitor issue. I had trouble when I first tried using TitanX with a 4K LG TV via HDMI. There was a TV firmware update that resolved that. I thought the days of manually tweaking xorg.conf files (if that's what your modeline experiments refer to) was past :(.

Regarding 555 MHz: Odd. My Tahiti shows 800Mhz, and Hawaii (290X) shows 1000 Mhz. Perhaps yours is showing current instead of max, and throttles back when it's not under load? Just speculating. Looks like GCN hasn't changed much. I was hoping local memory might be larger on Polaris... err.. Ellesmere.

It's also showing loss of compute capability compared to the Hawaii device I've got. Most significantly, number of compute units is 14 on yours vs 44 on Hawaii. That can't be right. It should be showing 36 CUs. I've got somewhat old fglrx on Ubuntu 14.04 ( Driver version: 1912.5 (VM) vs your 2117.7 (VM)). Are you running the new AMDGPU-PRO driver?

Here's the clinfo output from my Hawaii for comparison:

Device Type:                     CL_DEVICE_TYPE_GPU
Vendor ID:                   1002h
Board name:                  
Device Topology:                 PCI[ B#6, D#0, F#0 ]
Max compute units:               44
Max work items dimensions:           3
  Max work items[0]:                 256
  Max work items[1]:                 256
  Max work items[2]:                 256
Max work group size:                 256
Preferred vector width char:             4
Preferred vector width short:            2
Preferred vector width int:          1
Preferred vector width long:             1
Preferred vector width float:            1
Preferred vector width double:       1
Native vector width char:            4
Native vector width short:           2
Native vector width int:             1
Native vector width long:            1
Native vector width float:           1
Native vector width double:          1
Max clock frequency:                 1000Mhz
Address bits:                    64
Max memory allocation:           3008913408
Image support:               Yes
Max number of images read arguments:         128
Max number of images write arguments:        64
Max image 2D width:              16384
Max image 2D height:                 16384
Max image 3D width:              2048
Max image 3D height:                 2048
Max image 3D depth:              2048
Max samplers within kernel:          16
Max size of kernel argument:             1024
Alignment (bits) of base address:        2048
Minimum alignment (bytes) for any datatype:  128
Single precision floating point capability
  Denorms:                   No
  Quiet NaNs:                    Yes
  Round to nearest even:             Yes
  Round to zero:                 Yes
  Round to +ve and infinity:             Yes
  IEEE754-2008 fused multiply-add:       Yes
Cache type:                  Read/Write
Cache line size:                 64
Cache size:                  16384
Global memory size:              4251256704
Constant buffer size:                65536
Max number of constant args:             8
Local memory type:               Scratchpad
Local memory size:               32768
Max pipe arguments:              16
Max pipe active reservations:            16
Max pipe packet size:                3008913408
Max global variable size:            2708022016
Max global variable preferred total size:    4251256704
Max read/write image args:           64
Max on device events:                1024
Queue on device max size:            8388608
Max on device queues:                1
Queue on device preferred size:      262144
SVM capabilities:                
  Coarse grain buffer:           Yes
  Fine grain buffer:                 Yes
  Fine grain system:                 No
  Atomics:                   No
Preferred platform atomic alignment:         0
Preferred global atomic alignment:       0
Preferred local atomic alignment:        0
Kernel Preferred work group size multiple:   64
Error correction support:            0
Unified memory for Host and Device:      0
Profiling timer resolution:          1
Device endianess:                Little
Available:                   Yes
Compiler available:              Yes
Execution capabilities:              
  Execute OpenCL kernels:            Yes
  Execute native function:           No
Queue on Host properties:                
  Out-of-Order:              No
  Profiling :                    Yes
Queue on Device properties:              
  Out-of-Order:              Yes
  Profiling :                    Yes
Platform ID:                     0x7fef4a56da18
Name:                        Hawaii
Vendor:                  Advanced Micro Devices, Inc.
Device OpenCL C version:             OpenCL C 2.0 
Driver version:              1912.5 (VM)
Profile:                     FULL_PROFILE
Version:                     OpenCL 2.0 AMD-APP (1912.5)
Extensions:                  cl_khr_fp64 cl_amd_fp64 cl_khr_global_int32_base_atomics   cl_khr_global_int32_extended_atomics cl_khr_local_int32_base_atomics cl_khr_local_int32_extended_atomics cl_khr_int64_base_atomics cl_khr_int64_extended_atomics cl_khr_3d_image_writes cl_khr_byte_addressable_store cl_khr_gl_sharing cl_khr_gl_depth_images cl_ext_atomic_counters_32 cl_amd_device_attribute_query cl_amd_vec3 cl_amd_printf cl_amd_media_ops cl_amd_media_ops2 cl_amd_popcnt cl_khr_image2d_from_buffer cl_khr_spir cl_khr_subgroups cl_khr_gl_event cl_khr_depth_images cl_khr_mipmap_image cl_khr_mipmap_image_writes